EG is produced by the reaction of EO, producing MEG as the main product. MEG is predominantly used for the manufacture of polyester fibres, polyethylene terephthalate (PET) and, to a lesser extent, in the cooling systems of motor vehicles where it serves as antifreeze.
EG is produced in a combined EO/EG process, which provides very efficient heat integration. The integrated process is usually split up into four sections: EO reaction and CO2 removal plus EO recovery; light ends (LE) removal and EO purification; EC/MEG reaction and MEG recovery; and MEG purification.
In the EO reaction section EO is produced by reacting gaseous ethylene and oxygen on a catalyst at elevated temperature (200-300° C.) and pressure (15-20 bar). The reactions on the catalyst produce a considerable amount of heat, which is removed by generation of steam at the shell side of the reactor. The generated steam is used as heat medium in the plant.
In the EC/MEG reaction section, EO is reacted with CO2 to EC. In one system the reaction is carried out in two reactors EC-1 and EC-2 that are lined up in series and in which the bulk of the EO is converted. Residual EO can, if required, be converted in a tubular reactor, the EC finishing reactor. The EC-1 reactor produces approximately 24 kcal/gmole (100 kJ/gmole) of reaction heat at a temperature of about 100° C. This heat must be removed from the reactor via a side draw and cooling and recycle to the reactor. This is discussed in U.S. Pat. No. 6,080,897.
In the system of U.S. Pat. No. 6,080,897 the heat generated in the EC section is low temperature heat which cannot be stepped up to useful energy, e.g. for steam production. We have now found that it is possible to integrate heat between the EC-1 reactor and other units elsewhere in the plant, whilst still achieving the desired EC-1 Reactor temperature via cooling in the liquid recycle and chilled liquid production.